A preferred field of use of the filter membrane modules of interest combined in module racks is in apparatuses for water and waste water reprocessing, or industrial plants. Depending on each membrane type used, polluted liquids—in particular water—are cleaned of particles by filtration. Depending on each membrane type or preprocessing, separation of dissolved substances is also possible. The filtration method can be easily and safely carried out without the addition of chemicals and with very low energy expenditure. For this purpose, so-called filter membrane modules are used, which are usually elongate hollow cylinders serving as housings to accommodate filtration membranes. Modern filtration membranes comprise, for example, a plurality of individual porous capillary or flat membranes. The liquid to be filtered, referred to as raw water in the present case, is pressed into the capillary membranes, if these are used. The filtered liquid, referred to as the filtrate, passes through the porous walls. A filter membrane module comprises a bundle of a great number of individual filtration membranes. Usually the filter membrane module is integrated in a tube conduit system consisting of various supply and drain lines, through which the liquid to be filtered flows.
To dimension the membrane filter surface required for filtration to a predetermined throughput, a plurality of filter membrane modules are arranged in parallel. This is done in so-called module racks as a carrier structure. The module racks are racks which accommodate the filtration modules and their tube conduit system. In the ultra and micro filtration of interest here, in particular, the filter membrane modules containing the porous filtration membranes are backwashed at certain intervals to release and flush dirt adhering to the filtration membranes. For this purpose, filtered water is collected in advance.
JP 10323544 discloses a generic apparatus for backwashing filter membrane modules. An external backwashing reservoir is provided in this apparatus, in which water filtered in advance is collected. Pressurized air is used to press water from the reservoir against the filtration direction through the filtration modules. A drawback of this structure is that the backwashing reservoir must be provided as an additional component requiring additional structural space. There is also a risk of germ pollution in such a backwashing reservoir, if the filtrate kept therein stagnates for a longer period of time.
DE 10 2005 032 286 A1 discloses an alternative embodiment for an apparatus for backwashing filter membrane modules, which are arranged in module racks as in the generic structure. A plurality of individual filter membrane modules are provided arranged in a row, having a supply for the liquid to be filtered arranged at each of their two end faces. The supplies arranged at each end face are fed by collection lines extending transverse to the direction of extension of the individual filter membrane modules and along the module rack. The liquid to be filtered is pumped into these collection lines extending above and below the filtration modules and pressed through the filter membrane modules. Each filter membrane module further comprises at least one drain for the filtrate, which commonly opens out into one overhead filtrate collection line. From this filtrate collection line, the cleaned liquid is further drained.
For backwashing, a backwash reservoir arranged outside of the module rack and various further aggregates, such as a backwash pump, valves, controls and measuring sensors are necessary. The backwash pump, in particular, is a rather complex component. A further problem is, again, the risk of contamination and germ formation in the backwash reservoir due to the water often stagnating therein.
From U.S. Pat. No. 6,001,254 a technical solution can be derived, which dispenses with a backwashing reservoir for the backwashing process. Herein, individual filter membrane modules, which are not arranged in the form of a plurality of parallel-arranged module rows within a module rack, are sequentially backwashed with the filtrate of other filter membrane modules, in which each filter membrane module is treated individually at the time it is backwashed. Herein, the permeability of the thus individualized filter membrane module during backwashing and the permeability during operation of the rest of the filter membrane modules is determined with the aid of a water counter and pressure sensors to be able to form a diagnosis with respect to the periodicity of necessary backwashes, leaching of the filter membrane modules and operating anomalies.